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Employee benefits - Sensitivity analysis for actuarial assumptions (Details) - CAD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2022
Sep. 30, 2021
Actuarial assumption of discount rates | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ (19,249) $ (36,571)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ 20,234 $ 38,221
Actuarial assumption of discount rates | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ (2,294) $ (2,716)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ 2,500 $ 2,851
Actuarial assumption of discount rates | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ (1,512) $ (2,986)
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ 1,578 $ 3,144
Actuarial assumption of expected rates of salary increases | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 193 $ 480
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (188) $ (471)
Actuarial assumption of expected rates of salary increases | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 2,584 $ 2,870
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (2,388) $ (2,746)
Actuarial assumption of expected rates of salary increases | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 20 $ 35
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (19) $ (34)
Actuarial assumption of expected rates of pension increases | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 13,324 $ 25,254
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (12,614) $ (24,480)
Actuarial assumption of expected rates of pension increases | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 0 $ 0
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ 0 $ 0
Actuarial assumption of expected rates of pension increases | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 774 $ 1,440
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (747) $ (1,381)
Actuarial assumption of expected rates of inflation | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 21,301 $ 36,172
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (16,005) $ (34,478)
Actuarial assumption of expected rates of inflation | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 2,584 $ 2,870
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (2,388) $ (2,746)
Actuarial assumption of expected rates of inflation | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Percentage of reasonably possible increase in actuarial assumption 0.25% 0.25%
Percentage of reasonably possible decrease in actuarial assumption 0.25% 0.25%
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 774 $ 1,440
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (747) $ (1,381)
Actuarial assumption of life expectancy after retirement | U.K.    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Period of reasonably possible increase in actuarial assumption 1 year 1 year
Period of reasonably possible decrease in actuarial assumption 1 year 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 12,957 $ 27,907
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (13,093) $ (27,556)
Actuarial assumption of life expectancy after retirement | France    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Period of reasonably possible increase in actuarial assumption 1 year 1 year
Period of reasonably possible decrease in actuarial assumption 1 year 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 281 $ 555
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (320) $ (585)
Actuarial assumption of life expectancy after retirement | Germany    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Period of reasonably possible increase in actuarial assumption 1 year 1 year
Period of reasonably possible decrease in actuarial assumption 1 year 1 year
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption $ 1,511 $ 3,131
Increase (decrease) in defined benefit obligation due to reasonably possible decrease in actuarial assumption $ (1,360) $ (2,761)